May 03, 2005

Heterozygosity and attractiveness

According to a new study, men who are heterozygous at three loci of the major histocompatibility complex are judged to be more attractive by women. Such men may be more resilient to infection, and hence they might live longer, or infect their spouses and offspring less; therefore, women may have evolved a preference for the phenotypical cues of MHC-heterozygous males, and such males have come to be seen as more attractive.

Females gain direct or indirect fitness benefits by choosing between males with traits indicating “good genes,” but we usually know very little about the nature of these genes. However, it has been suggested that genetic quality may often be defined as heterozygosity at certain loci. Here, we show that heterozygosity at three key loci in the major histocompatibility complex (MHC) is associated with facial attractiveness: Faces of men who are heterozygous at all three loci are judged more attractive by women than faces of men who are homozygous at one or more of these loci. MHC genes code for proteins involved in immune response. Consistent with this function, faces of MHC heterozygotes are also perceived to be healthier. In a separate test, in the absence of any other cues, patches of skin from the cheeks of heterozygotes are judged healthier than skin of homozygotes, and these ratings correlate with attractiveness judgements for the whole face. Because levels of MHC similarity can influence mate preferences in animals and humans, we conducted a second experiment with genotyped women raters, finding that preferences for heterozygosity are independent of the degree of MHC similarity between the men and the female raters. Our results are the first to directly link facial attractiveness and a measure of genetic quality and suggest a mechanism to help explain common consensus concerning individual attractiveness. In a relatively monogamous species like humans, evolutionary benefits from choosing heterozygous mates could include prolonged parental care and reduced risk of contracting disease for females and their offspring.

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